US3916309A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Short circuit capacity measuring device
Assignee: S&C Electric Co
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Filing: 1974-09-30
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Granted: 1975-10-28
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Expires: 1994-09-30
Abstract
Abstract Disclosed is an electrical test instrument consisting fundamentally of a shunt capacitor for test connection to an electrical power system or circuit along with auxiliary circuits which include a control circuit to turn on at peak voltage following a manual actuation in order to allow a peak detector circuit to measure or otherwise determine the maximum instantaneous value of inrush current to the shunt capacitor from the power system, the inrush current being a function of the available short-circuit current capacity at a given location of the power system. The purpose of the instrument is to ascertain the magnitude of the short-circuit current available at any selected location on a power system and thereby select the proper short-circuit interrupting rating for a protective device such as a fuse or circuit breaker without the need for heretofore required time-consuming engineering calculations.
Inventors
- 👤 John F Foulkes
- 👤 John S Ferguson
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-02 10:27
CPC Classifications
G; G01; G01R; G01R19/00; G01R19/04
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
239 words
A device for measuring the short-circuit current capacity at any location on an electrical power circuit comprising: a capacitor; a resistor connected in series combination with said capacitor, said series combination of said capacitor and said resistor having a first terminal and a second terminal, said series combination of said capacitor and said resistor being connected by said first terminal and said second terminal across the line of the electrical power circuit; peak detector means connected across said resistor for detecting the peak voltage drop across said resistor; indicating means connected to said peak detector for indicating the short-circuit current capacity of the circuit under test corresponding to the peak voltage drop across resistor detected by said peak detector means; electronic switch means connected in series between said first terminal and said resistor, said electronic switch means having a non-conducting state for preventing current flow through said combination of said resistor and said capacitor, and said electronic switch means capable of switching to a conducting state to permit current to flow from said first terminal to said second terminal through said combination of said resistor and said capacitor in response to receipt of a control signal; control means for providing a control signal to said electronic switch means in response to external operator initiation thereby causing said electronic switch means to switch from its non-conducting state to its conducting state at the peak voltage of the electrical power circuit.
Claim 2
Independent Claim
239 words
A device for measuring the short-circuit current capacity at any location on an electrical power circuit comprising: a capacitor; a resistor connected in series combination with said capacitor, said series combination of said capacitor and said resistor having a first terminal and a second terminal, said series combination of said capacitor and said resistor being connected by said first terminal and said second terminal across the line of the electrical power circuit; peak detector means connected across said resistor for detecting the peak voltage drop across said resistor; indicating means connected to said peak detector for indicating the short-circuit current capacity of the circuit under test corresponding to the peak voltage drop across resistor detected by said peak detector means; electronic switch means connected in series between said first terminal and said resistor, said electronic switch means having a non-conducting state for preventing current flow through said combination of said resistor and said capacitor, and said electronic switch means capable of switching to a conducting state to permit current to flow from said first terminal to said second terminal through said combination of said resistor and said capacitor in response to receipt of a control signal; control means for providing a control signal to said electronic switch means in response to external operator initiation thereby causing said electronic switch means to switch from its non-conducting state to its conducting state at the peak voltage of the electrical power circuit.
Claim 3
Dependent Claim
80 words
A device for measuring short-circuit current capacity as claimed in claim 1, wherein said control means comprises a zero crossing detector means for detecting when the voltage of said electrical power circuir crosses the zero axis following external operator initiation and a timing means for providing a control signal to said electronic switch means at approximately one-fourth of the cycle of voltage wave form in said electrical power circuit after the voltage of said electrical circuit crosses the zero axis.
Claim 4
Dependent Claim
38 words
A device for measuring short-circuit current capacity as claimed in claim 2 wherein said timing means provides said control signal to said electronic switch means 4 milliseconds after the voltage of said electrical circuit crosses the zero axis.
Claim 5
Dependent Claim
58 words
A device for measuring short-circuit current capacity as claimed in claim 1 wherein said control means comprises: a phase shifting means for shifting the voltage on the circuit 90* out of phase; a zero crossing detector means for detecting and providing a control signal to the electronic switch means when the 90* out-of-phase signal crosses the zero axis.
Claim 6
Dependent Claim
22 words
A device for measuring short-circuit current capacity as claimed in claim 1 wherein said electronic switch means comprises a silicon controlled rectifier.
Claim 7
Dependent Claim
20 words
A device for measuring short-circuit current capacity as claimed in claim 1 wherein said electronic switch means comprises a triac.
Claim 8
Dependent Claim
46 words
A device for measuring short-circuit current capacity as claimed in claim 1 wherein said indicator means comprises an electrical meter for measuring the peak voltage across said resistor detected by said peak detector means and visually indicating the corresponding short-circuIt current capacity of the electrical circuit.
Claim 9
Dependent Claim
138 words
A device for measuring short-circuit current capacity as claimed in claim 1 wherein said indicating means comprises: a second electronic switch means connected to said first terminal; a level detector means connected to said peak detector for detecting when the peak voltage level detected by said peak detector exceeds a pre-determined level; an isolation circuit means connected to said level detector for providing a control signal to said second electronic switch means for causing said electronic switch means to switch from its non-conducting state to its conducting state when the level detector means detects a peak voltage level that exceeds the pre-determined level; and an indicator lamp electrically connected to said second electronic switch means and to the second terminal so that said indicator lamp will light when the second electronic switch means switches to its conducting state.
Claim 10
Dependent Claim
41 words
A device for measuring short-circuit current capacity as claimed in claim 8 further comprising an audible alarm electrically connected to said second electronic switching device for providing an audible alarm when said second electronic switching device switches to its conducting state.
Claim 11
Dependent Claim
30 words
A device for measuring short-circuit current capacity as claimed in claim 1 further comprising switch means for discharging said capacitor after said electronic switch means switches to its non-conducting state.
Claim 12
Independent Claim
25 words
A device for measuring short-circuit current capacity as claimed in calim 1 wherein said resistor can be adjusted to vary the resistance of said resistor.
Claim 13
Dependent Claim
33 words
A device for measuring short-circuit current capacity as claimed in claim 9 wherein said indicator lamp and said audible alarm are electrically connected to said second electronic switching device by a variable transformer.
References Cited (Backward Citations)
US1975065A
Cited
US2870407A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-10-27 | 1979-04-28 | 1979-10-28 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-10-27 | 1983-04-28 | 1983-10-28 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-10-27 | 1987-04-28 | 1987-10-28 | $7700.00 | Window Closed / Lapsed |